Field
The disclosed concept relates to charging ram assemblies for electrical switching apparatus, such as, for example, circuit breakers. The disclosed concept also relates to pin assemblies for charging ram assemblies. The disclosed concept further relates to methods of securing pin members within charging ram assemblies.
Background Information
Electrical switching apparatus, such as circuit breakers, provide protection for electrical systems from electrical fault conditions such as, for example, current overloads, short circuits, abnormal voltage and other fault conditions. Typically, circuit breakers include an operating mechanism, which opens electrical contacts to interrupt the flow of current through the conductors of an electrical system in response to such fault conditions as detected, for example, by a trip unit. The electrical contacts include stationary electrical contacts and corresponding movable electrical contacts that are separable from the stationary electrical contacts.
Among other components, the operating mechanisms of some low and medium voltage circuit breakers, for example, typically include charging ram assemblies that are used to store potential energy and release the potential energy to close the electrical contacts. The charging ram assemblies of many known circuit breakers commonly include a ram member, a guide pin, and a nut. During assembly, the nut is torqued onto an end of the guide pin and then riveted to hold the nut in place. In order to use the riveting process, the hardness of the guide pin must be undesirably limited. Because of the reduced hardness to accommodate the riveting process, mechanical endurance testing has shown that the rivet fails earlier than desired. More specifically, the force of the ram member causes the threads of the relatively soft guide pin to break or deform, causing the nut to slide with respect to the guide pin and the entire assembly to elongate. As a result, the ram member over-travels beyond its desired finish location and causes rigid components in the circuit breaker to be undesirably impacted.
There is thus room for improvement in charging ram assemblies, and in pin assemblies and securing methods therefor.